With an estimated 200 cases of hydatid disease per 100,000 population, northwestern Kenya has the highest prevalence of echinococcosis in the world. In some areas of Turkana District, virtually every resident is exposed to E. granulosus. For some, hydatid infection results in life- threatening morbidity due to hepatic, pulmonary, cardiac, skeletal, or gastrointestinal dysfunction. Because of limited health care in the region and the recent reduction of control programs, hydatid disease represents a major public health problem for the Kenyan Health Service. No study has examined the course of echinococcal disease from infection to the development of cysts. For this reason there are no data on the development of immunologic responses to this disease and their possible contribution to eradication of the parasite or progression of disease. This project has 3 interrelated goals. The first goal is to define the natural history of echinococcal infection by regular demographic, clinical and serologic surveys in a population where the prevalence is high. All stages of hydatid disease will be represented in this population. The second objective is to construct cDNA libraries (derived from human as well as sheep parasites) from which a panel of clones encoding E. granulosus-specific antigens and antigens associated with specific stages of disease will be identified and produced by recombinant DNA technology. Finally, sera collected from the study population will be used to define the humoral immunological response to parasite antigens using standard serological assays, newly developed immunoblotting assays, single antigen ELISAs, and isotype and antigen capture assays. Emphasis will be placed on identifying antigens and developing assays capable of predicting disease activity and cyst viability during infection and after spontaneous or therapeutic cure.